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Thank you Tony, and more boring stuff...

June 9 2008 at 2:51 AM

Response to Rachael... this is the BEST explanation of it's operating theory...

I would be happy to provide a paragraph or two for "Best of", and I would shorten the essay below with "you need the diodes, trust me."

Ok, you asked why the diodes are needed...The reason for the diodes is quite subtle. If we had just one pod motor, diodes would not be needed. Elsewhere, Eric has kindly posted a pic of the two cam switches. It can be seen that there is always at least one switch that connects to the motor, and for most of the time, both switches connect to the motor. The reason for the diodes is this:

The two motors are independent machines, and thus will always be slightly different in performance, e.g. one might run slightly slower than the other. Imagine we had no diodes, just straight wires. Everything would be fine if the two motors always ran and parked precisely together every time. However, if say the left hand motor gets a bit tired and gets just a tiny bit out of phase with the other, this makes the right hand one park first, but the other is still powered and running. The l/h running motor, by virtue of the cam switches and the wiring between the two motors, also provides power back to the r/h motor, which means it will be "kicked" out of its park position and off it would go again, looking for the next park position. While it's doing this, it powers the l/h motor again, so it can't park itself.

Thus, without the diodes to stop the undesired power connections between the two motors, we would have had non-stop winking cars within a few nights of leaving the factory.

I think you can replace the four diodes with two 5 pin changeover relays, or four 4 pin relays, but that would be a tricky wiring job and a step backwards in technology. Modern diodes are tough and easy to solder, so people shouldn't be afraid of them.

Cheers R

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